Hair dyes for dyeing hair are widely used as, for example, "gray hair dyes" and "fashion dyes". These hair dyes are generally classified as "temporary hair dyes" which are for temporary hair dyeing, "semi-permanent hair dyes" which give a semi-permanent hair dyeing effect and "permanent hair dyes" which give a permanent hair dyeing effect.
These hair dyes, as a matter of course, contain a coloring agent to dye the hair to a desired color. For this coloring agent, an "acidic dye" which exhibits the best hair dyeing effect in the acidic pH region is one of the most preferable because it has superior safety as a coloring agent for hair dye. Particularly for the coloring agent for "semi-permanent hair dyes" which are designed to have a semi-permanent hair dyeing effect, azo type acidic dyes are mainly used. Therefore, there is a great need for acidic dyes for hair dyes.
When using "acidic hair dyes" which have this acidic dye for the coloring agent, the pH has to be adjusted to the strongly acidic region of 1.5-4.5 and a thickener is commonly added to keep this strongly acidic hair dye from dripping and touching something other than the hair.
However, the selection of the thickeners which can be used in this strongly acidic pH region is fairly limited and even the thickeners which are said to be usable in the strongly acidic region are not necessarily satisfactory on the whole as thickeners to be added to hair dyes.
That is, an example of the main thickeners currently used in acidic hair dyes is xanthan gum (Japanese examined patent publication Tokko Hei 2-32253). A system in which bentonite and/or cross-linked sodium polyacrylate is used in addition to xanthan gum for improved performance (Tokko Hei 2-32253) has also been used.
However, conventionally known hair dyes with added xanthan gum, while they are certainly stable around pH 4.0-5.0, their viscosity significantly changes, resulting in a stability problem, in the strongly acidic region of pH 1.5-4.0. Also, it cannot be denied that the flowability is poor and, when scooped up on a hand and applied to the head, it tends to drip off as a lump and spreading it onto the hair tends to be difficult. Also, it gives a sticky feeling when used and hence is not satisfactory in terms of sensation of touch at the time of use.
Because of this, a system in which bentonite and or cross-linked sodium polyacrylate is used in addition to xanthan gum was discovered to improve the aforementioned flowability. However, there still is a problem in stability and also a problem has arisen in that it takes a long time and effort to wash it off after use.
Among the aforementioned "permanent hair dyes", "oxidation hair dyes" which develop colors by making an oxidizing agent act on an oxidation dye have a particularly permanent effect and have a bleaching effect as well to make the color tone of the hair brighter than it was originally. Because of this, they are among the most commonly used hair dyes.
This oxidation hair dye usually takes the form of the two formulation type comprising the formulation (I) which contains the oxidation dye and the formulation (II) which contains the oxidizing agent (the powder type is a one formulation type because it utilizes air oxidation). In the two formulation type hair dye, formulation (I) is used to make the low molecular weight oxidation dye penetrate into the hair and then formulation (II) is used to initiate oxidation polymerization of the oxidation dye in the hair and on the hair surface so as to produce pigments and complete the dyeing process.
However, although the oxidation hair dyes conventionally used have a superior hair dyeing ability, they have a problem in that when they are used the hair is damaged, loses moisture and gloss and combing becomes difficult. Furthermore, although they are called "permanent hair dyes", they have a tendency to gradually fade through exposure to sunlight and/or the use of shampoo. Therefore, an oxidation hair dye with superior fastness is desired. Various investigations have been conducted so far to make up for these shortcomings, but none has been recognized as producing a satisfactory result.
For example, an attempt was made to solve these problems by blending dextrin pullulan, which is a polysaccharide, into the oxidation hair dye (Japanese examined patent publication Tokko Hei 4-3206). However, although the use of dextrin pullulan did provide good dye-affinity, the fastness against sunlight and or washing was not sufficient and the problem of "damaged hair" was not completely solved. Also, dextrin pullulan caused a problem in stability over time depending on the oxidation hair dye system. It must be said therefore that dextrin pullulan had some unsuitable characteristics for blending in an oxidation hair dye composition.
Therefore, the object of the present invention is to provide a hair dye composition which has superior characteristics compared to the aforementioned conventional technology. Specifically, the following can be listed as the objects:
The first object is to provide an acidic hair dye composition which is stable even in the strongly acidic pH region (pH 1.5-4.0), has a high flowability, has superior feeling at the time of use and is thickened in such a way that washing-off after use does not require too much time and effort.
The second object is to provide an oxidation hair dye composition which has significantly improved dyeability and improved fastness against sunlight and/or washing, reduces hair damage down to very little, gives gloss to the hair and has superior stability over time.